This book constitutes the refereed proceedings of the 4th International Conference on Extreme Programming and Agile Processes in Software Engineering, XP 2003, held in Genova, Italy in May 2003. The 33 revised full papers presented together with experience reports, research reports, abstracts from an educational symposium and a PhD symposium, as well as panel statements were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on managing agile processes, methodological issues, extending agile methodologies and XP, methods and tools, teaching and education aspects, testing, pair programming, and other XP practices.